Giving fibre supplements to patients with a history of growths in their colon may actually increase rather than reduce the problem.

Many doctors believe that most colorectal cancer develop out of polyps, or adenomas, which grow on the wall of the bowel.

Previous studies had suggested that giving people extra soluble fibre in granule form, such as ispaghula husk, could reduce the growth of polyps, and thus colorectal cancer.

However, the latest research, conducted in France, Denmark, Italy and Germany, suggests that new adenomas are actually more likely to grow in patients given this fibre supplementation.

There is no new evidence, however, that fibre taken naturally in the diet, from vegetables or other sources, could be causing a problem.

In 552 patients with a history of polyps, roughly a third each were given extra fibre, extra calcium, or nothing at all.

New probe

Three years later, the patients were given a second colonoscopy to see if any new polyps had appeared.

In the group given no supplements, 36 out of 178 had new polyps, while 58 out of 198 in the fibre group had new growths.

However, in those given calcium supplementation, only 28 out of 176 had new polyps.

A diet rich in fresh vegetables is thought to protect bowel health

There is still clear evidence that diet has a major role in the development of colorectal cancer, which is one of the biggest cancer killers in the UK.

In particular, high consumption of red meat is associated with a higher risk of developing this form of cancer.

Some other studies have suggested that eating vegetables, whole-grain cereals and calcium have a protective effect.

Dr Tim Key, expert on diet and cancer with Imperial Cancer Research Fund,
said:
"Colorectal adenomas are growths in the large intestine which are not
cancerous, but some adenomas do eventually grow and turn into cancers.

"This trial indicated that neither calcium nor ispaghula husk reduced the
development of new adenomas.

"The increased number of adenomas in the
patients receiving ispaghula husk is of some concern, but should not be
interpreted as evidence that dietary fibre in general might be harmful.

"Therefore the recommendation remains that healthy diets should be high in
vegetables, fruits and cereals."
He added: "This trial has no clear implications for the development of colorectal
cancer, because most adenomas do not turn into cancers."